Overview:
The non-lineaged human, a blank canvas which brings no expectations but no guidance. The lingeaged have personality traits that they are encouraged to follow but the non-lineaged do not. They are similar to the human race in many RPG systems, no real downside from playing them but no real upside either. This means, when dealing with RP effects, they are neither resistant or weak to them, they are effected normally.

A new player may find them easier to start off with as they don’t have to do things such as show great anger as they would if they were a changeling. Some may find a defining characteristic useful however, as it helps them get into character a lot more easily.

Trappings:
With trapping, it’s more about avoiding accidently taking the trappings that are associated with those of lineage. It is unlikely that one would accidently take goat horns and be mistaken as a cambion, however one might wear white make up and be mistaken for a draughir.

Having no trappings will make a first costume slightly cheaper and easier to produce but perhaps less interesting.

Acceptance:
The non-lineaged are more likely to be accepted in everyday society. They are the norm and so don’t have to worry as much about discrimination.

With eternals, they may find that those with lineages of the eternal’s realm, are favoured. This could effect deals you make with said eternals but this shouldn’t be too much of a problem. (inset name of the eternal who is doing experiments on the lineage) is an example where this will not be the case. She views lineages as imperfections and seeks to remove them. As a non-lineaged you will safe in her presence which could have some benefits.

The blood:
The non-lineaged have blood like a regular human. They have no strange properties and are what you expect. The non-lineaged can give birth to those with lineage. This can happen for many different reasons.

Decent into madness:
The vortex that is madness still afflicts the non-lineaged. There is no specific way they will act once this madness has claimed them, instead it is, as it was before, up to the person playing the character to decide how they should act.

Trappings: Unlineaged humans are often seen wearing hats, hoods, circlets and other similar clothing that would be made awkward by horns or the other more obvious trappings of lineage.

On the other hand, it is very much not done for an unlineaged person to mimic lineage with face-paint or fake horns - if a character would wish to pretend to be lineaged, given that a common illusion of Night can fake lineage with great accuracy, anything less would be unacceptable. [Out of character, please do not have your character pretend to be lineaged with simple makeup which could not be mistaken for the real thing in character - the route for this is the Night ritual ‘Twilight Masquerade’]

Roleplaying effects: Unlineaged humans often find it easier to get up in the morning than most other lineages, often (although not always) enjoying a simpler and easier morning routine than those of dramatic and outlandish appearance.

Humans in the Empire have been told for centuries that they literally superior to the tainted lineage, The Orcs, and any other species. It even states as much in our own religious doctrine. Playing a character that was brought up with these thoughts does make sense regardless of recent history.

You are a human living only sixty years after the end of the recognition as “people” and emancipation of Orcs. Many people you know will be pretty racist about Orcs. The vast majority of the Empire is likely to be at least a well meaning unintentional racist about Orcs.

To balance that the Highguard brief does specifically state this in the “what they are not” section.

Zealots or Bigots. There are zealots in Highguard but as a nation they strive to be righteous and lead by example; they are not self-righteous and condemnatory.

So I think if you’re giving people advice on “how to play a human” you’d need to dial back telling them that most of them are racist. It’s something of a cliche at this point, when most people playing humans on the field are generous to a fault to lineage and orc characters.

Also the idea of lineage being a “taint” is literally not part of doctrine. Lineaged humans are still humans, so the Doctrine of Human Destiny applies to them as well, and there is no official doctrine on the influence of the Realms.

Unlineaged Urizeni might have an inferiority complex towards the lineaged, looking down only on briars for their anti-intellectual impulses. Or they might be defensive about it, pointing out their versatility compared to a merrow or their get-up-and-go attitude compared to a naga.

Meanwhile the Dawnish will sometimes set harder tests for the Lineaged, not because they don’t like them but because they do. A Changeling with a lust for Glory literally written into their skin should be expected and demanded to do better than their unlineaged sibling, no?

Navarri or Winterfolk… well, apart from the well known Navarri prejudice against briars… it’s pragmatic. You are what you do.

In Highguard, you’re quite right, an unlineaged person will have been brought up knowing that they didn’t have the (perceived) natural inclination away from Virtue that haunts the lineaged. But actual flaming bigotry would verge upon the false virtue of Hatred, against which the Virtuous must gird themselves at least as strongly as the influence of the Realms…